In recent years, mobile applications, such as portable electronic devices, multimedia products, wireless communications and so forth demand high-speed and high-throughput computations. Thus, memory speed goes up higher and channel counts between a control module and a memory continue to increase. However, faster data rate and switching speed imply that higher coupled noise may be caused among adjacent signal channels (transmission lines).
FIG. 1 is a schematic diagram illustrating a parallel bus configuration between a control module and a memory circuit. As shown in FIG. 1, a memory bus 12 between the control module 11 and the memory 13 includes many signal channels which are very close to each other.
Crosstalk is the effect on a signal caused by the high-speed switching of a nearby signal, and crosstalk can be a major contributor to the amount of jitter. Once a large amount of jitter exists in the signal channel, bit errors in the channel transmission signal may cause. Alternatively speaking, crosstalk between adjacent signal channels may cause distortion and suppression of crosstalk is important, and crosstalk can be a major contributor of the jitter. With the high density of signal channels included in the memory bus 12, crosstalk issue between adjacent signal channels becomes serious.
FIGS. 2A and 2B are schematic diagrams illustrating termination resistors are used to suppress crosstalk. In these figures, each of the receivers 15, 16 includes a buffer circuit 15a, 16a and a termination resistor Rter. The buffer circuits 15a, 16a convert a channel transmission signal received from the signal channels to an inverted channel transmission signal (buffered channel transmission signal) at a receiving terminal Nrv, and the termination resistors Rter are often utilized to suppress crosstalk between adjacent channels.
In FIG. 2A, the termination resistor Rter conducts a receiving terminal Nrv to a source voltage Vddr and a dc current always flows through the buffer circuit 15a if an input of the buffer circuit 15a is at a high voltage level (for example, the source voltage level Vddr). In FIG. 2B, the termination resistor Rter conducts the receiving terminal Nrv to a ground voltage Gnd, and a dc current always flows through the buffer circuit 16a if an input of the buffer circuit 16a is at a low voltage level (for example, the ground voltage level Gnd).
Accompanied with the dc currents, the output signals of the receivers 15, 16 are biased, and swing ranges of the output signals are affected. Furthermore, the dc currents flowing through the buffer circuits 15a, 16a and the termination resistors Rter may cause extra power consumption.